Every year many persons are involved in traffic-related accidents resulting in injury or death. In order to reduce the number of accidents and/or to reduce their impact, vehicle safety systems have been developed.
Protective safety systems, such as bumpers, seat belts, crumple zones and air-bags have been in use for many years. They work by dispersing the kinetic energy resulting from a collision in order to protect the occupants of the vehicle.
In addition to the protective safety systems, another type of safety systems has been introduced in the recent years. These in-vehicle systems are designed to help the driver to prevent, avoid or mitigate an impending collision or accident. They are therefore called preventive safety systems. Advanced preventive safety systems work by not only sensing the motion of vehicle hosting the system but also perceiving the traffic situation around the vehicle. They are able to inform the driver of possible danger, to warn the driver of an impending accident, and to detect and classify dangerous situations. In addition, the system may actively assist or intervene in the operation of the vehicle in order to avoid the accident or mitigate its consequences.
A collision avoidance system is an example of a preventive safety system. If a collision is likely to occur and the system detects that the driver does not react in an appropriate manner, the system may be adapted to apply an emergency operation and/or to warn the driver. For example, when the system determines that a collision is unavoidable, it may apply an autonomous brake to the vehicle. If the speed is too high to be able to avoid the obstacle ahead, e.g. a lead vehicle, the system may at least help to lower the speed in order to reduce the consequences of the collision. As described herein, the term collision avoidance system is used for systems adapted to avoid collisions as well as systems mitigating the consequences of a collision. Often, the difference between whether a collision is avoided or not depends on the speed of the host vehicle and the relative speed to the obstacle.
The term host vehicle is herein used to refer to the vehicle which hosts an onboard perception system. The term onboard means that the system is adapted to be used in or on a vehicle. Normally an onboard perception system forms a part of a collision avoidance system as explained below. The term lead vehicle is used to refer to the vehicle located closest to and in front of the host vehicle. Normally the lead vehicle is driving in essentially the same direction as the host vehicle.
In general, a collision avoidance system comprises three separate subsystems: a perception system, a detection system and an action system. The perception system comprises different sensors, which are used to determine the motion of the host vehicle and to perceive the traffic situation therearound. The detection system uses the output of the perception system in order to detect possible adverse situations and make a decision to inform, warn or intervene. The action system executes the action or actions decided by the detection system.
The execution of a possible intervention is a trade-off between effectiveness of the collision avoidance system and the risk of having a false intervention. It is for example undesirable that the collision avoidance system brakes the host vehicle without there actually being a real emergency situation.
In rush-hour-traffic, the traffic is often dense and the time-gap between vehicles can be small. The collision avoidance system can help the driver by continuously or intermittently assessing the distance between the own vehicle, i.e. the host vehicle, and the lead vehicle, i.e. a vehicle in front of the host vehicle. If the host vehicle comes too close to the lead vehicle, the collision avoidance system may actively intervene in order to avoid a collision or at least to mitigate its consequences.
Document DE 10 2006 040 651 A1 discloses a vehicle collision detection device. The device uses a non-directional airborne sound sensor system to characterize a collision object. This information is combined with information from an impact sound sensor. The information may be used to activate a personal protection means, such as an airbag, belt tightener or an active seat. An independent claim is also included for a method for detecting a collision between the vehicle and a collision object.
The system of DE 10 2006 040 651 A1 thus detects an already occurred collision between the host vehicle itself and another object. However, the purpose of a collision avoidance system is to avoid the collision or at least mitigate its consequences. It would thus be too late if the collision first occurs and thereafter is detected.
Current collision avoidance systems rely on their perception systems to refine noisy sensor measurements regarding the position and velocity of a lead vehicle, e.g. radar measurements. These perception systems employ filters to reduce the dynamics of lead vehicle position and velocity signals in order for the collision avoidance system to be robust against sensor anomalies. However, in situations where something unexpected happens to the lead vehicle, such as the lead vehicle being involved in a collision, it is difficult to distinguish a sensor anomaly from the fact that the lead vehicle actually has suddenly changed its motion, e.g. abruptly being brought to a stand still, based on the sensor observations. In such situations, the dynamic behavior is significantly different from what is expected in normal traffic situations and a conventional perception system will therefore face difficulties in such a situation.
It is thus desirable to provide an onboard perception system being robust against sensor anomalies and yet having appropriate performance in high dynamic situations, such as when the tracked vehicle is involved in a collision.